Polymers containing nitrile and thioamide groups and their preparation

ABSTRACT

Novel polymers containing nitrile and thioamide groups are prepared by contacting a polymer of acrylonitrile or vinylidene cyanide with hydrogen sulfide at a temperature below about 50* C in the presence of a catalytic amount of an alkali metal carbonate. The polymers are useful as coatings and in the preparation of fibers and films.

United States Patent Picklesimer Aug. 29, 1972 [54] POLYMERS CONTAININGNITRILE AND THIOAMIDE GROUPS AND THEIR PREPARATION [72] Inventor:Lewellyn G. Picklesimer, Dayton,

Ohio

[73] Assignee: The United States of America as represented by theSecretary of the United States Air Force [22] Filed: Feb. 2, 1971 [21]Appl.No.: 112,021

[52] U.S. Cl. ..260/79.5 NV, 260/79.7, 260/778 [51] Int. Cl. ..C08f27/06 [58] Field of Search.....260/79.5 R, 79.5 NV, 79.5 C,

260/778, 78.4 N, 88.7 B, 55 IS, 79.7

[56] References Cited UNITED STATES PATENTS 1,984,417 12/1934 Mark..260/2 2,280,578 4/1942 Hanford ..260/55 1 2,563,640 8/1951 Brown..260/79.5 C 2,563,662 8/1951 Rothrock ..260/79.5 C 2,891,932 6/ l 959Hankins ..260/80.73 2,893,908 7/1959 Antlfinger 1 54/ l 39 3,346,63210/1967 Tull ..260/55l Primary ExaminerJoseph L. Schofer AssistantExaminer-C. A. Henderson, Jr. Att0rney-Harry A. Herbert, Jr. and CedricH. Kuhn [57] ABSTRACT 12 Claims, No Drawings I POLYMERS CONTAININGNITRILE AND THIOAMIDE GROUPS AND THEIR PREPARATION FIELD OFTHE'INVENTION This invention relates to polymers that contain nitrileand thioamide groups. In one aspect it relates to a process forpreparing such polymers.

BACKGROUND OF THE INVENTION reactivity rates, sequential feeding of themonomers to the reaction zone may be required. For a more completediscussion of the difficulties encountered in the copolymerizationprocess, reference is made to Copolymerization by Alfrey, Bohrer andMark, Interscience Publishers, New York, N. Y., 1952.

It is an object of this invention, therefore, to provide a polymercontaining nitrile and thioamide groups that is more soluble in commonsolvents than polyacrylonitrile or copolymers of acrylonitrile and anethylenically unsaturated compound.

Another object of the invention is to provide a process for preparing apolymer containing nitrile and thioamide groups.

Other objects and advantages of the invention will become apparent tothose skilled in the art upon consideration of the accompanyingdisclosure.

wherein R is l CEN or S=C-NH2 and R is hydrogen,

CEN or S=( NHz at least a portion of the R and R groups being Broadlyspeaking, the polymers of this invention are 2 iii \v iLiLiiii I I EN/nL I D-NH; 1 1 /EN I 1 til-NH:

As shown in the above equation, n is equal to three and a mol ofhydrogen sulfide has reacted with each of two nitrile groups to give apolymer containing one nitrile group and two thioamide groups. Theproduct can also be described as containing two thioacrylamide and oneacrylonitrile moieties or units. 1

' The following equation represents for purposes of illustration thereaction that occurs when using. a polymer of vinylidene cyanide as thestarting material:

According to the above equation, n is equal to three and a mol ofhydrogen sulfide has reacted with each'of three nitrile groups to give apolymer containing three nitrile groups and three thioamide groups.

The polymeric starting materials generally. have a relatively highmolecular weight so that n in the form ulas is usually a whole number inthe range of about 500 to 3,000 and higher. The number of recurringunits in the polymer product in general corresponds to those in thestarting materials, i.e., in the range of about 500 to 3,000 and higher.In general, it is preferred to use as starting materials thosepolymersof acrylonitrile and of vinylidene cyanide which are recognizedin the art as being fiber-formable polymers. Likewise the polymerproducts of this invention can be described as being fiber-formablepolymers.

The terms polymers of acrylonitrile and polymers of vinylidene cyanideas used herein to designate the starting materials are intended toinclude homopolymers as well as copolymers of acrylonitrile and ofvinylidene cyanide and an ethylenically unsaturated compound. Examplesof suitable copolymerizable monomers include acrylic acid, methacrylicacid, acrylates, such as methyl acrylate, ethyl acrylate, butylacrylate, methyl methacrylate, ethyl methacrylate, and butylmethacrylate, vinyl chloride, vinyl bromide, vinylidene chloride, vinylcarboxylates, such as vinyl acetate, vinyl chloracetate, and vinylpropionate, and the like. Generally, the copolymer contains at leastweight percent of acrylonitrile or vinylidene cyanide, e.g., from 80 to98 weight percent acrylonitrile or vinylidene cyanide and 2 to 20 weightpercent of the ethylenically unsaturated compound.

When a copolymer is used as the starting material, the comonomer unitsin the polymer chain remain unaffected as a result of the addition ofthe hydrogen sulfide. In other words, the polymer is employed as thestarting material. This is illustrated by the following equation whichshows the reaction that occurs when a I copolymer of acrylonitrile andmethyl methacrylate is the starting material:

As seen from the above equation, a copolymer having n acrylonitrile andm methyl methacrylate randomly distributed units is contacted withhydrogen sulfide. Furthermore, x mols of hydrogen sulfide reacts with alike number of nitrile groups, giving x number of thioacrylamide unitsand n-x number of acrylonitrile units. The number m of methylmethacrylate units remains unchanged. It is, of course, understood thatthe three different types of units are randomly distributed throughoutthe polymer chain.

From the foregoing discussion it is seen that when the starting materialis a copolymer, the polymers of this invention can be specificallydefined as comprising recurring units having the following formula:

l l i H wherein R is R is hydrogen, I

-CEN or S=CNH2 at least a portion of the R and R groups being and Z is arandomly distributed moiety resulting from the polymerization of anethylenically unsaturated compound. The Z moieties usually constituteabout 2 to 20 weight percent of the polymer.

As previously mentioned, the process of this invention involves thecontacting of a polymer of acrylonitrile or vinylidene cyanide withhydrogen sulfide. I a preferred embodiment the process comprises thestep of contacting the polymer with hydrogen sulfide, the polymer beingin solution in a solvent and the contacting occurring in the presence ofan alkali metal carbonate catalyst at'a temperature below about 50 C,e.g., between about 20 and 50 C.

Examples of suitable solvents that can be used includedimethylformamide, dimethylacetamide, and dimethylsulfoxide. In thepractice of the process, the polymeric starting material is initiallydissolved in the solvent so as to form a dilute solution. It has beenfound to be convenient to work with solutions containing about 5 toweight percent polymer although higher concentrations can be usedwithout adverse effects. The polymer solution is conveniently made up ina gas tight vessel fitted with a stirrer, an inlet for gaseous hydrogensulfide, an outlet for unreacted hydrogen sulfide, and a thermometerwell.

Hydrogen sulfide gas is bubbled slowly through the solution withvigorous stirring. It has been found that the addition of the hydrogensulfide to the nitrile groups occurs rapidly and efficiently atatmospheric pressure and room temperature, i.e., at about 20 C. This wassurprising because the conversion of simple nitriles to thioamides byhydrogen sulfide addition as taught by the prior art exemplified by US.Pat. Nos. 2,280,578 and 2,421,031 requires elevated temperatures andhigh pressures. It has also been found that in the present process, thetemperature of the reaction mixture must not exceed about 50 C. If thetemperature is permitted to rise above about 50 C, the polymercrosslinks, forming an insoluble mass.

The addition of hydrogen sulfide is usually continued for a period offrom about 7% to 10 hours. However, the reaction period will generallydepend upon the number of nitrile groups that it is desired to convertto thioamide groups. the higher the molecular weight of the polymericstarting material the longer the time required to convert the number ofnitrile groups necessary to obtain a product of increased solubility. Asan indication of when the polymer has attained a desired solubility, ithas been found to be convenient to continue the addition of hydrogensulfide until 1 milliliter of the polymer solution is completelymiscible in 10 milliliters of acetone. The starting materials prior tohydrogen sulfide addition are insoluble in acetone. An indication ofadditional substitution of thioamide groups and a further increase insolubility may be obtained by continuing to add hydrogen sulfide until 1milliliter of the polymer solution is completely miscible in methylethyl ketone, another non-solvent for the starting materials. While itis theoretically possible to convert all of the nitrile groups tothioamide groups, as a practical matter about 20 to percent of thenitrile groups are usually converted. One mol of hydrogen sulfide isrequired for each nitrile group that is to be converted to a thioamidegroup. I actual practice it is usually preferred to add an excess amountof hydrogen sulfide, e.g., 1.25 to 1.75 mol per nitrile group to beconverted. By operating with an excess of hydrogen sulfide, good contactbetween that material and the nitrile groups is assured, therebyhastening the addition.

After the addition of hydrogen sulfide is completed, the polymer productis recovered from solution by any suitable means, such as byprecipitation. In a preferred method, the product is recovered bypouring the solution into water, thereby causing the polymer toprecipitate from solution. The precipitated polymer can then beseparated by filtration or decantation after which it is dried. It isoften desirable to pour the polymer solution into water contained in amixing vessel, such as a Waring blendor, so as to wash the product. Theproduct is usually air dried initially with the drying being completedunder vacuum at room temperature since it is somewhat hygroscopic.

While the process of this invention can be conducted in the absence of acatalyst, it is preferred to utilize such a material. Thus, it has beendiscovered that the addition of hydrogen sulfide to the nitrile groupcan be promoted by conducting the process in the presence of a catalyticamount of an alkali metal carbonate, such as sodium, potassium orlithium carbonate. As used, the

catalyst is preferably in finely powdered form. Furthermore, it has beenfound that when dimethyl sulfoxide is used as the solvent, the use of acatalyst is necessary. Thus, in the absence of a catalyst, thedimethylsulfoxide reduces the hydrogen sulfide to sulfur and addition tothe nitrile groups does not occur. The amount of catalyst used can varywithin rather wide limits, e.g., from about 1 to weight percent of thepolymeric starting material. However, it is usually preferred to employabout 2 to 5 weight percent of the catalyst. In using the catalyst, ithas been found to be advantageous to add it to the polymer solutionseveral hours, e.g., from about 8 to 16- hours, prior to addition of thehydrogen sulfide.

A more complete understanding of the invention can be obtained byreferring to the following illustrative examples which are not intended,however, to be unduly limitative of the invention.

EXAMPLE I A run was carried out in which 300 grams of polyacrylonitrilewas dissolved in 3,985 grams of dimethylformamide. This was accomplishedby adding the polymer to a flask containing the solvent. The flask usedin this and succeeding examples was fitted with a gas inlet, an outlet,an efficient stirrer and a thermometer. Hydrogen sulfide was bubbledthrough the polymer solution. During addition of the hydrogen sulfide,the solution was stirred rapidly to ensure thorough mixing of thematerials. In this run and the runs described in the succeedingexamples, the reaction temperature was maintained at below 35 C bycooling the flask with water. Addition of hydrogen sulfide was continuedfor a total of 10 hours before 1 ml. of the product solution was solublein 10 ml. of acetone. Thereafter, the polymer solution was added towater in a Waring blendor thereby precipitating the polymer. The productwas then separated and washed with running water after which it was diedin air. A small sample was dried in a vacuum desiccator. The driedsample was then analyzed, and the following are the results of theelemental analysis:

Weight percent Carbon 58.36 Nitrogen 21.44 Sulfur 10.66 Hydrogen 6.] l

The foregoing analysis indicates that about 22 percent of the nitrilegroup of the polyacrylonitrile were converted thioamide groups.

EXAMPLE II The addition of hydrogen sulfide was continued for anadditional 4 hours. The product was recovered and dried a in Example I.A sample of the product was analyzed with the following results:

Weight percent Carbon 55.57 Nitrogen 2 l I9 Sulfur l2.86 Hydrogen 6. I 8

The foregoing analysis indicates that about 26 percent of thepolyacrylonitrile were converted to thioamide groups.

EXAMPLE III Weight percent Carbon 62.57 Nitrogen 24.06 Sulfur 6.93Hydrogen 5.8 l

The foregoing analysis indicates that about 13 percent of the nitrilegroups of the polyacrylonitrile were converted to thioamide groups. Thisis about the lower limit of conversion at which the product is solublein acetone.

EXAMPLE IV A run was carried out in which 50 grams of polyacrylonitrilewas dissolved in 950 grams of dimethylsulfoxide. Hydrogen sulfide wasslowly bubbled through the solution while vigorously stirring. After 5hours 1 ml. of the solution was only partially miscible in 10 ml. ofacetone. The reaction flask was stoppered and allowed to standovernight. The next morning it was observed that yellow crystals hadseparated out of the solution. Analysis of the crystals proved them tobe sulfur. After sitting for 48 hours, the solution was still onlypartially miscible with acetone. The polymer product was recovered as inExample I, washed and dried. An analysis of the product indicated thatit contained L44 weight percent sulfur.

EXAMPLE V run was conducted in which 50 grams of polyacrylonitrile wasdissolved in 950 grams of dimethylsulfoxide. To the solution there wasthen added with stirring 2.5 grams of sodium carbonate. The addition ofhydrogen sulfide was COMMENCED and after 1 hour 1 ml. of the solutionwas miscible with 10 ml. of acetone. After addition of hydrogen sulfidehad been continued for one more hour, 1 ml. of the solution was misciblewith 10 ml. of methyl ethyl ketone. The addition of hydrogen sulfide wascontinued for a total of hours. Thereafter the polymer was recovered anddried as in Example I. A sample of the product was analyzed with thefollowing results:

from the flask, and the polymer product was separated therefrom as inExample I, washed and dried. A sample of the product was analyzed withthe following results:

Weight percent Weight percent Carbon 45.73 Carbon 59.06 Nitrogen 17.42Nitrogen 21.02 2:52;... is as 10 Oxygen 4.32

The foregoing anal sis indicates that about 69 ercent of the nitrilegroup: of the polyacrylonitrile weEe con- The g g analySl? mdlcates thatabout percent of verted to thioamide group. An infrared spectra which 5the mmle groups m the copolymer product were conwas taken confirmed thepresence of the thioamide verted to thl9amlde groups groups. Theremainder of the solution in the flask was allowed to sit overnight. Thenext morning the addition EXAMPLE VI of hydrogen sulfide was continuedfor a period of 5 A run was conducted in which 50 grams of 20 3; l igg mg2:3 2: iz iz ggigz iig fglgg polyacrylonitrile was dissolved in 950grams of anabized with the following results. dimethylformamide. To thesolution there was then added with stirring 2.5 grams of lithiumcarbonate. The weight percent addition of hydrogen sulfide was commencedand after about 2 hours 1 ml. of the solution was miscible with 10carbon 54 7 ml. of acetone. After addition of hydrogen sulfide hadNitrogen 19.47 been continued for one more hour, 1 ml. of the solution 52-8; was miscible with 10 ml. of methyl ethyl ketone. The oi gzfipolymer product was recovered as in Example l, washed and dried. Ananalysis of the product gave the following resultsl The above analysisindicates that about 37 percent of the nitrile groups in the copolymerproduct were con- Weight Percent verted to thioamide groups.

Polymers of acrylonitrile are insoluble in both Carbon 50.48 acetone andmethyl ethyl ketone. The runs described in 2133f the foregoing examplesshow that the polymers of this Hydrogen invention containing nitrile andthioamide groups are soluble in both of these materials. This propertyof the 40 polymers renders them particularly useful in the The foregoinganalysis indicates that about 50 percent 'f f f fibers Moreover hPolymer prodflcts of the nitrile group of the polyacrylonitrile wereconof thls mvemlon C311 8150 be ed In preparlng coatings verted tothioamide groups. and F As will be evident to those skilled in the art,various EXAMPLE VII modifications of this invention can be made in thelight f the foregoing disclosure without departing from the A run wasconducted in which grams of o polyacrylonitrile was dissolved in 950grams of gj g ofthe mvemlon' dimethylformamide. To the solution therewas then L A plymer sonsisting essentially of a plurality of added withstirring 2.5 grams of potassium carbonate. 50 repeating units having thefollowing formula: The addition of hydrogen sulfide was commenced andafter 45 minutes 1 ml. of the solution was miscible with g g 10 ml. ofacetone. After addition of hydrogen sulfide \H 31/ had been continuedfor an additional 30 minutes, 1 ml. wherein R1 is N or S:C NH2 and R2 ishydr0 of the solution was miscible with 10 ml. of methyl ethyl en, C E Nr S=CNH if fg l if gz zggsg gg was recovered as m EX b from about 20 to80 percent of the R ad R groups eing EXAMPLE VIII S H 2 A run wascarried out in which 996 grams of a copolymer of acrylonitrile andmethylmethacrylate sald polymer bemg Slubl.em 9 (90-l0) was dissolved in7,000 grams of dimethylfor- The polymer accordmg to clalm 1 m which R118mamide. To the solution there was then added with stir- 1 ring 24.9grams of sodium carbonate. The addition of C:N or S=C NH hydrogensulfide was then commenced. After about 3 hours 1 ml. of the solutionwas miscible with 10 ml. of acetone. About one-half of the solution wasremoved and R is hydrogen.

3. The polymer according to claim 2 in which 20 to percent of said R,groups are 4. The polymer according to claim 1 which consistingessentially of a plurality of repeating units having the followingformulas:

6. A process for preparing a polymer having nitrile and thioamide groupswhich comprises the steps of contacting with hydrogen sulfide gas apolymer having nitrile groups selected from the group consisting ofpolymers of acrylonitrile and polymers of vinylidene cyanide, saidpolymers being in solution in a solvent selected from the groupconsisting of dimethylformamide, dimethylacetamide and dimethylsulfoxideand said contacting occurring in the presence of a catalytic amount ofan alkali metal carbonate at a temperature below about 50 C.; andcontinuing said contacting until about to 80 percent of the nitrilegroups are converted to thioamide groups.

7. The process according to claim 6 in which said polymer is a polymerof acrylonitrile. 8. The process according to claim 6 in which saidpolymer is a copolymer of acrylonitrile and methylmethacrylate.

9'. The process according to claim 6 in which said polymer is a polymerof vinylidene cyanide.

10. The process according to claim 6 in which said polymer is dissolvedin said solvent, said catalyst is added to the resulting solution, saidhydrogen sulfide is bubbled through said solution for a period of fromabout one half to 10 hours, and said polymer having nitrile andthioamide groups is recovered from said solution.

11. The process according to claim 10 in which said polymer havingnitrile and thioamide groups is recovered by contacting said solutionwith water, thereby precipitating said polymer.

12. The process according to claim 6 in which said catalyst is sodium,potassium or lithium carbonate and the amount of catalyst used is about1 to 10 weight percent of said polymer.

2. The polymer according to claim 1 in which R1 is and R2 is hydrogen.3. The polymer according to claim 2 in which 20 to 80 percent of said R1groups are
 4. The polymer according to claim 1 which consistingessentially of a plurality of repeating units having the followingformulas:
 5. The polymer according to claim 1 in which R1 and R2 arefrom about 20 to 80 percent of the R1 and R2 groups being
 6. A processfor preparing a polymer having nitrile and thioamide groups whichcomprises the steps of contacting with hydrogen sulfide gas a polymerhaving nitrile groups selected from the group consisting of polymers ofacrylonitrile and polymers of vinylidene cyanide, said polymers being insolution in a solvent selected from the group consisting ofdimethylformamide, dimethylacetamide and dimethylsulfoxide and saidcontacting occurring in the presence of a catalytic amount of an alkalimetal carbonate at a temperature below about 50* C.; and continuing saidcontacting until about 20 to 80 percent of the nitrile groups areconverted to thioamide groups.
 7. The process according to claim 6 inwhich said polymer is a polymer of acrylonitrile.
 8. The processaccording to claim 6 in which said polymer is a copolymer ofacrylonitrIle and methylmethacrylate.
 9. The process according to claim6 in which said polymer is a polymer of vinylidene cyanide.
 10. Theprocess according to claim 6 in which said polymer is dissolved in saidsolvent, said catalyst is added to the resulting solution, said hydrogensulfide is bubbled through said solution for a period of from about onehalf to 10 hours, and said polymer having nitrile and thioamide groupsis recovered from said solution.
 11. The process according to claim 10in which said polymer having nitrile and thioamide groups is recoveredby contacting said solution with water, thereby precipitating saidpolymer.
 12. The process according to claim 6 in which said catalyst issodium, potassium or lithium carbonate and the amount of catalyst usedis about 1 to 10 weight percent of said polymer.